LC BIOLOGY- The Digestive System

Herbivores

animals that feed mainly on plants

Carnivores

animals that feed mainly on animals

Omnivores

animals that feed on plants and animals

Autotrophs

organisms that make their own food

Heterotrophs

organisms that take in food from the environment

Parasites

take in their food from a live source

Saprophytes

take in their food from a dead source

Associative Digestive Glands

• salivary glands

• liver and gall bladder

• pancreas

Digestion

the physical and chemical breakdown of food

Ingestion

the taking of food into the digestive system

Physical Digestion

• the mechanical breakdown of food

• takes place when we chew food or churn it in the stomach

Mechanical Digestion

takes place in the mouth by the chewing and grinding action of teeth on food

Chemical Digestion

the breakdown of food using enzymes

Absorption

occurs when the digested food passes from the digestive system and enters into the blood

Egestion

the removal of unabsorbed waste from the digestive system

Incisors

• found at the front of the mouth

• shaped like chisels to cut and slice food

Canines

• long, pointed, fang-like teeth

• used to grip and tear food

Premolars

large, flat surfaces and are used to crush and grind food

Molars

• large teeth located at the back of the mouth

• crush and grind food

Dental Formula

2 ( I ²⁄₂ C ¹⁄₁ P ²⁄₂ M ³⁄₃ )

Amylase

breaks down starch to form maltose

Pharynx

connects the mouth to the oesophagus

Epiglottis

closes over the trachea and ensures the food passes down the oesophagus

Peristalsis

a wave of muscular action in the walls of the alimentary canal that moves the contents along

Fibre

stimulates peristalsis

Mucus

coats the stomach and prevents self-digestion

Pepsinogen

an inactive enzyme that is converted to the active enzyme pepsin by acid in the stomach

Pepsin

an enzyme that converts proteins to smaller peptides

Protease

an enzyme that digests protein (e.g. pepsin)

Hydrochloric Acid

• gives the stomach a pH of 1 to 2

• kills bacteria, loosens fibrous and cellular foods, activates pepsinogen, denatures salivary amylase

Pancreas

secretes the hormone insulin and digestive materials

Lipase

an enzyme that acts on lipids, products are fatty acids and glycerol

Liver

• breaks down red blood cells

• makes bile

• detoxifies the body

• breaks down excess amino acids to form urea

Hepatic Portal Vein

blood vessel that carries digested nutrients away from the digestive system

Bile

a liquid made in the liver and stored in the gall bladder

Functions of Bile

• to emulsify lipids

• to neutralise chyme from the stomach

• to excrete pigments

Small Intestine

consists of two main parts: the duodenum and the ileum

Duodenum

its main function is digestion

Amylase

made in : salivary glands

active in : mouth

substrate : starch

product : maltose

preferred pH : 7 to 9

Pepsin

made in : stomach lining

active in : stomach

substrate : protein

product : peptides

preferred pH : 2

Amylase

made in : pancreas

active in : duodenum

substrate : starch

product : maltose

preferred pH : 7 to 9

Lipase

made in : pancreas

active in : duodenum

substrate : lipids

product : fatty acids and glycerol

preferred pH : 7 to 9

Ileum

its function is to absorb nutrients

Carbohydrates

are digested to monosaccharides (e.g. glucose)

Lipids

are digested to fatty acids and glycerol

Villi

line the walls of the duodenum and ileum

Adaptations of the Villi for Absorption

• large numbers (increase the surface area)

• walls are only one cell thick

• have a rich blood supply

Deamination

any amino acids not used by the body are broken down in the liver, forming urea

Lacteal

• inside each villus

• contains a liquid called lymph

• fats are transported away by lymph

Adaptations of the Small Intestine for Absorption

• very long

• numerous villi and microvilli (increasing the surface area)

• walls of the villi are very thin

• rich blood supply to carry away water-soluble products

• each villus has a lacteal to carry away the fats

Caecum

• the part of the large intestine below its junction with the small intestine

• appendix is found at the end

Vestigial Organs

have lost their former use (e.g. the caecum and appendix)

Colon

its function is to reabsorb water

Symbiotic Bacteria

beneficial bacteria that live in the human digestive tract

Functions of Symbiotic Bacteria

• produce some B group vitamins and vitamin K

• break down food, especially cellulose

• prevent the growth of pathogenic bacteria and fungi

Rectum

stores faeces

Balanced Diet

contains all the necessary food types in the correct proportions